The proteins in question are vitellogenins: analogues of vertebrate apoB, a component of low-density lipoprotein (LDL). In the clk-1 worm mutant, an increase in the levels of an antioxidant results in less oxidation of lipoprotein. The result is a slowing in germline development.
The slowed development is reversed by blocking the production of lipoproteins, or by reestablishing a more normal level of oxidation by reactive oxygen species (ROS). “The degree of oxidation is a measure of general metabolism,” says Hekimi. “The germline may want to know that the worm is running fast. It could be sensing the general quality of metabolism.” ROS effects on signaling have been seen before in vitro, but the new results are the most dramatic to be detected in vivo.
The effects of lipoproteins on germline development go through a receptor-associated kinase called ARK-1. Although ARK-1 is known to work downstream of an EGF-like receptor, it is not clear whether this or another type of receptor is a mediator for the lipoprotein signal, or which lipoprotein species (oxidized or nonoxidized) is doing the signaling. ▪